Published Aug. 9, 1997|Updated Oct. 1, 2005

A day spent spading cartloads of mulch or compost about the garden or yard can produce physical symptoms more severe than an aching back, researchers warn.

The complex mixture of plant, bacterial and fungal products can result in organic dust toxic syndrome, characterized by fever, inflamed lung passages, tightness of chest and airway obstruction.

Dr. Paul Blanc, chief of occupational and environmental medicine at the University of California at San Francisco, and colleagues documented the inflammatory effect of mulch dust on the lungs of a group of volunteers who shoveled wood chips from a pile for an hour or two.

Although only one of six volunteers actually became ill, two others had some symptoms and three of the six showed marked increase in lung inflammation during followup testing, Blanc and his colleagues reported in a recent issue of the Journal of Occupational and Environmental Medicine.

The findings match other research that has found people seem to vary in their reactions to the airborne toxins from mulch and other organic compounds, with some getting sick almost every time they're exposed, others never getting sick, and many falling in between.

"We got into this after a friend of mine who is a gardener asked me why, every so often after a day of heavy work, he'd develop a fever and feel like he was coming down with the flu," Blanc said.

In most cases, unless an allergic reaction is involved, the effects pass in 24 hours or so, which is why many sufferers mistake the syndrome for a flu bug. Although other, more serious, pneumonialike illnesses can be spawned on rare occasions from exotic fungi in some mulch, the lungs seem able to clear themselves of the irritations of most organic dust without any medical intervention, the researcher said.

The National Institute for Occupational Safety and Health estimates that as many as 30 percent to 40 percent of agricultural workers exposed to organic dusts come down with the flulike illness.

Most studies have focused on agricultural workers inhaling dust from cotton, hay, silage, grain and animal confinements such as barn stalls and poultry coops, but the condition also has been observed in people working with sawdust, wood chips and compost piles.

"Usually, four to six hours after exposure, the person feels achy, they have a chill and develop a fever of maybe 101 or greater," Blanc said. "They typically go to bed feeling like they have the flu and wake up in the morning feeling better."

Blanc said most weekend gardeners have little to worry about from mulch dust but suggests that people concerned about it "try to work with fresh, damp material that hasn't had time to grow a lot of bacteria and mold.

"The less dust raised, the better, so don't try to fling great shovelfuls of the stuff many feet across the yard," he added. "Use a cart to get the chips where you need them and apply them gently."